1. Field
The invention concerns a process for the production of water-soluble, naturally folded and secreted polypeptides after expression in prokaryotic cells.
2. Description
Protein synthesis in prokaryotic organisms, which is also called translation, takes place on the ribosomes in the cytoplasm. When recombinant DNA is expressed in prokaryotic host organisms, it is often desirable to secrete the recombinant gene product or protein that is obtained in this process from the cytoplasm through the inner bacterial membrane into the periplasmic space between the inner and outer membrane. Secreted proteins can then be released from the periplasm into the nutrient medium for example by osmotic shock. A disadvantage of this process is that the secreted polypeptides often do not form the native, biologically active conformation (Hockney, TIBTECH 12 (1994) 456-463; Baynex, Curr. Opin. Biotechnol. 10 (1999) 411-421).
Compounds such as urea or urea derivatives, formamide, acetamide or L-arginine are used in methods for the in vitro renaturation of insoluble protein aggregates (inclusion bodies) which are formed during the cytoplasmic expression of recombinant DNA in prokaryotic cells. L-arginine as an additive can considerably improve the yield of natively folded proteins in the renaturation in vitro (Rudolph et al., U.S. Pat. No. 5,593,865; Buchner & Rudolph, Bio/Technology 9 (1991)157-162; Brinkmann et al., Proc. Natl. Acad. Sci USA 89 (1992) 3075-3079; Lin & Traugh, Prot. Express. Purif. 4 (1993) 256-264). Thiol reagents such as glutathione are known to improve the yield of natively folded proteins when recombinant DNA is expressed in prokaryotic cells (Glockshuber et al., EP-A 0 510 658).
Recently molecular chaperones and folding catalysts such as peptidyl-prolyl-cis/trans-isomerases or protein disulfide isomerases (Glockshuber et al., EP-A 0 510 658) have been used to increase the yield of native recombinant protein when folded in vivo (Thomas et al., Appl. Biochem. Biotechnol. 66 (1997) 197-238). In some cases this has led to considerable improvements in the expression e.g. of ribulose bisphosphate carboxylase (RUBISCO; Goloubinoff et al., Nature 337 (1989) 44-47), human procollagenase (Lee & Olins, J. Biol. Chem. 267 (1992) 2849-2852) or neuronal nitrogen oxide synthase from rats (Roman et al., Proc. Natl. Acad. Sci. USA 92 (1995) 8428-8432). In these examples GroEL/ES or the DnaK system from E. coli was co-overexpressed in the cytosol. The positive effect is usually an increased yield of the desired protein in a soluble form.
The co-expression of chaperones has also been examined when recombinant proteins are secreted into the periplasm of E. coli. However, in this case only a cytosolic overexpression of chaperones was evaluated in order to optimize secretion into the periplasm (Perez-Perez et al., Biochem. Biophys. Res. Commun. 210 (1995) 524-529; Sato et al., Biochem. Biophys. Res. Commun. 202 (1994) 258-264; Berges et al., Appl. Environ. Microbiol. 62 (1996) 55-60). Molecular chaperones are used in the prior art to stabilize proteins and thus to protect them from aggregation and inactivation (Buchner et al., EP-A 0 556 726 A1). Previous attempts at cosecretion in E. coli have only concerned folding catalysts, such as protein disulfide isomerase (PDI; Glockshuber et al., EP-A 0 510 658) or peptidyl-prolyl-cis/trans-isomerases or Dsb proteins from E. coli (Knappik et al., Bio/Technology 11 (1993) 77-83; Qiu et al., Appl. Environm. Microbiol. 64 (1998) 4891-4896 and Schmidt et al., Prot. Engin. 11 (1998) 601-607). Recently, co-overexpression of the periplasmic Skp protein led to more efficient folding of phase display and higher yield of antibody fragments secreted to the periplasm (Bothman and Plutckthun, Nat. Biotechnol. 16 (1998) 376-380; Hayhurst and Harris, Prot. Expr. Purif. 15 (1999) 336-343).